The present invention relates to the protection of the teeming stream or flow of a molten metal contained in a vessel and passing through a plate-type valve or cut-off mechanism of the kind comprising a stationary plate and a displaceable plate that is provided with at least one output nozzle.
These valve or cut-off mechanisms control the opening and closing of the outlet of the receiver, foundry ladle, or distributor that contains the molten metal, the output nozzle being arranged to be placeable in communication with outlet. They consequently allow the casting of the molten metal, e.g. steel, into an ingot mould or the like. The casting of the molten metal may be performed directly from the ladle into the ingot mould or, in the case of a continuous casting process, from the ladle into a distributor and thereafter into the ingot mould.
The two plates consist of a material made to resist high temperatures, such as impregnated or resinified ceramic or alumina. The displaceable plate may be slidable or rotatable and may be provided with a single output nozzle or several nozzles differing in internal diameter. In the latter case, the pouring speed may be modified by changing the nozzle, for example in relation to the height of metal in the vessel or container. The two plates may be urged against each other by means of a system of springs provided with a cooling circuit.
It is known moreover that it is of importance to prevent any contact between ambient atmospheric air and molten metal during a teeming or casting operation, to avoid the forming of any of various oxides within the metal mass, these oxides considerably altering the quality of the end product.
The cut-off devices known up to now have numerous points of passage for atmospheric air which is actually drawn in by the suction engendered by the outflow of molten metal. Such valve or cut-off devices increase the risk of air bubble occlusion in the metal during the casting operation and consequently the risks of oxidisation.
The points at which the air reaches the metal are: the gap between the two mutually confronting surfaces of the stationary and displaceable plates, due to the play required for their reciprocal displacement; the area of connection between the nozzle(s) and the displaceable plate, in particular when said nozzle(s) is (are) removably fitted on said plate; the outlet end of the nozzle; the connection between the stationary plate and the container as well as--in the case the nozzles permanently fitted on the displaceable plate--the connection between said nozzle and said plate, these connections being established by "grouting" with a thin mortar which by its nature is only a poor sealant, which offers only a low degree of gas-tightness and becomes increasingly porous as cracks appear after a period of use.
It is an object of the invention substantially to eliminate or minimise the aforesaid disadvantages.